Its occupation by M23 forced the government army, the FARDC, into a humiliating retreat from Goma and several other towns that surround it.

"We are leaving for peace," Sultani Makenga, the rebels' military commander, said as he watched a cadre of 40 of his troops prepare to leave.

Their withdrawal was a condition of talks mediated by Yoweri Museveni, Uganda's president, that will now open the path to deeper negotiations about the rebel army's grievances.

The M23 is made up of deserters from Congo's national army, who mutinied in April, complaining that they were not being paid and their officers were being passed over for promotion.

It is not clear when or where the next round of peace discussions will be held.

A unit of 100 M23 soldiers will stay in Goma at its strategically important airport, which they will control alongside state forces.

"I am happy to see that there is some progress away from the direction of fighting," said Christian Kabori, a student in Goma.

"But truly will there be long-lasting peace? That we cannot tell. The M23 must get so many concessions or they will come back to take Goma again, that is what we worry about." There was no word from Rwanda on the rebels' withdrawal. The government there has been accused of supporting the M23 with financing, troops and weapons, which it denies.

Britain last week suspended a new tranche of aid worth £21 million that was due to be given to Rwandan president Paul Kagame this month.

There was "credible and compelling evidence" of Rwanda's meddling in this latest conflict in eastern Congo, the British government said.